The present invention is in the field of electrical power generating and, more particularly, electrical power generating systems (EPGS) that may be subjected to electrical overloading.
In some applications of EPGS's, electrical loading may produce electrical power that exceed available power deliverable to a shaft of a generator of the EPGS. An aircraft power system may be one example of such an application of an EPGS. In an aircraft, a shaft driven generator may be powered with a turbine engine. Conditions may arise, during operation of the aircraft, when electrical power demands increase rapidly. In some cases, these demands, or increases in electrical load may exceed the shaft power available to drive the generator. The generator-driving engine may become overloaded and lose speed. In extreme cases, the engine may stall and require re-starting.
In the prior-art, overload protection systems were employed to reduce or prevent engine overloading resulting from excessive increases in electrical loading. Prior art protection systems provide temporary electrical disconnection of excessive electrical load from the generator. Such temporary disconnection may occur for a time interval sufficient to allow the electrical load to decrease. After the electrical load reaches an acceptably reduced level, the load is then re-applied to the generator.
In an operating aircraft, a loss of electrical power may be catastrophic. Consequently, prior art protection systems provide mechanisms for avoiding a total absence of electrical power during the temporary disconnection period. For example, batteries or banks of capacitors (so-called supercapacitors) may provide temporary electrical power. However, in these prior-art overload protection systems, a certain time delay may be experienced before an alternate source of electrical power becomes available to the electrical load. This is because it is necessary to recognize a need for and then connect these alternate sources of electrical power to the load. Typically, this recognition and connecting process occurs through switching arrangements that require a finite time period for completion. This may result in a brief but nevertheless finite period of time when the electrical load is not provided with electrical power. Transition from one source to another without interruption is not a trivial task. Transient behavior may create serious disturbances to the loads that are connected to the bus. In addition, as is the case with almost any aircraft electrical component, the presence of batteries or supercapacitors may add undesired weight and a need for complex wiring interconnection within the aircraft.
As can be seen, there is a need to provide a protection system for an EPGS that prevents engine overloading without a loss of electrical power to an excessive electrical load. Additionally, in the case of an aircraft, there is a need to provide such a protection system without adding weight or external wiring interconnections to the aircraft.